.img {
  width: 350px;
  height: 350px;
  position: relative;
  background: url('./imgs/1.jpg');
}

.mask {
  width: 50px;
  height: 50px;
  background-color: yellow;
  opacity: .5;
  position: absolute;
  left: 0px;
  top: 0px;
}

.enlarge {
  width: 100px;
  height: 100px;
  background: url('./imgs/1.big.jpg');
  background-position: 0px 0px;
}